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Soby Mathew523d6332015-01-08 18:02:19 +00001/*
Govindraj Rajaeee28e72023-08-01 15:52:40 -05002 * Copyright (c) 2015-2020, Arm Limited and Contributors. All rights reserved.
Varun Wadekard3ad4c72018-06-29 13:34:51 -07003 * Copyright (c) 2020, NVIDIA Corporation. All rights reserved.
Soby Mathew523d6332015-01-08 18:02:19 +00004 *
dp-armfa3cf0b2017-05-03 09:38:09 +01005 * SPDX-License-Identifier: BSD-3-Clause
Soby Mathew523d6332015-01-08 18:02:19 +00006 */
7
Soby Mathew523d6332015-01-08 18:02:19 +00008#include <assert.h>
Soby Mathew523d6332015-01-08 18:02:19 +00009#include <string.h>
Antonio Nino Diaze0f90632018-12-14 00:18:21 +000010
11#include <arch_helpers.h>
12#include <lib/bakery_lock.h>
13#include <lib/el3_runtime/cpu_data.h>
14#include <lib/utils_def.h>
15#include <plat/common/platform.h>
Soby Mathew523d6332015-01-08 18:02:19 +000016
17/*
18 * Functions in this file implement Bakery Algorithm for mutual exclusion with the
19 * bakery lock data structures in cacheable and Normal memory.
20 *
21 * ARM architecture offers a family of exclusive access instructions to
22 * efficiently implement mutual exclusion with hardware support. However, as
23 * well as depending on external hardware, these instructions have defined
24 * behavior only on certain memory types (cacheable and Normal memory in
25 * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
26 * in trusted firmware are such that mutual exclusion implementation cannot
27 * expect that accesses to the lock have the specific type required by the
28 * architecture for these primitives to function (for example, not all
29 * contenders may have address translation enabled).
30 *
31 * This implementation does not use mutual exclusion primitives. It expects
32 * memory regions where the locks reside to be cacheable and Normal.
33 *
34 * Note that the ARM architecture guarantees single-copy atomicity for aligned
35 * accesses regardless of status of address translation.
36 */
37
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010038#ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
39/*
40 * Verify that the platform defined value for the per-cpu space for bakery locks is
41 * a multiple of the cache line size, to prevent multiple CPUs writing to the same
42 * bakery lock cache line
43 *
44 * Using this value, if provided, rather than the linker generated value results in
45 * more efficient code
46 */
Elyes Haouas183638f2023-02-13 10:05:41 +010047CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0,
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010048 PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple);
49#define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE)
50#else
51/*
52 * Use the linker defined symbol which has evaluated the size reqiurement.
53 * This is not as efficient as using a platform defined constant
54 */
Varun Wadekar77c382c2019-01-30 08:26:20 -080055IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_START__, BAKERY_LOCK_START);
56IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_END__, BAKERY_LOCK_END);
57#define PERCPU_BAKERY_LOCK_SIZE (BAKERY_LOCK_END - BAKERY_LOCK_START)
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010058#endif
Soby Mathew523d6332015-01-08 18:02:19 +000059
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000060static inline bakery_lock_t *get_bakery_info(unsigned int cpu_ix,
61 bakery_lock_t *lock)
62{
63 return (bakery_info_t *)((uintptr_t)lock +
64 cpu_ix * PERCPU_BAKERY_LOCK_SIZE);
65}
Soby Mathew523d6332015-01-08 18:02:19 +000066
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000067static inline void write_cache_op(uintptr_t addr, bool cached)
68{
69 if (cached)
70 dccvac(addr);
71 else
72 dcivac(addr);
Soby Mathew523d6332015-01-08 18:02:19 +000073
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000074 dsbish();
75}
76
77static inline void read_cache_op(uintptr_t addr, bool cached)
78{
79 if (cached)
80 dccivac(addr);
Varun Wadekard3ad4c72018-06-29 13:34:51 -070081
82 dmbish();
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000083}
Soby Mathew523d6332015-01-08 18:02:19 +000084
Soby Mathewf9baaa52016-11-14 17:19:35 +000085/* Helper function to check if the lock is acquired */
Okash Khawaja66b7fdc2022-04-08 18:06:31 +010086static inline __unused bool is_lock_acquired(const bakery_info_t *my_bakery_info,
Masahiro Yamada019b4f82020-04-02 15:35:19 +090087 bool is_cached)
Soby Mathewf9baaa52016-11-14 17:19:35 +000088{
89 /*
90 * Even though lock data is updated only by the owning cpu and
91 * appropriate cache maintenance operations are performed,
92 * if the previous update was done when the cpu was not participating
93 * in coherency, then there is a chance that cache maintenance
94 * operations were not propagated to all the caches in the system.
95 * Hence do a `read_cache_op()` prior to read.
96 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000097 read_cache_op((uintptr_t)my_bakery_info, is_cached);
98 return bakery_ticket_number(my_bakery_info->lock_data) != 0U;
Soby Mathewf9baaa52016-11-14 17:19:35 +000099}
100
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100101static unsigned int bakery_get_ticket(bakery_lock_t *lock,
Masahiro Yamada019b4f82020-04-02 15:35:19 +0900102 unsigned int me, bool is_cached)
Soby Mathew523d6332015-01-08 18:02:19 +0000103{
104 unsigned int my_ticket, their_ticket;
105 unsigned int they;
106 bakery_info_t *my_bakery_info, *their_bakery_info;
107
108 /*
109 * Obtain a reference to the bakery information for this cpu and ensure
110 * it is not NULL.
111 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100112 my_bakery_info = get_bakery_info(me, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000113 assert(my_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000114
Soby Mathewf9baaa52016-11-14 17:19:35 +0000115 /* Prevent recursive acquisition.*/
116 assert(!is_lock_acquired(my_bakery_info, is_cached));
Soby Mathew156280c2015-02-20 16:04:17 +0000117
118 /*
Soby Mathew523d6332015-01-08 18:02:19 +0000119 * Tell other contenders that we are through the bakery doorway i.e.
120 * going to allocate a ticket for this cpu.
121 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000122 my_ticket = 0U;
Soby Mathew523d6332015-01-08 18:02:19 +0000123 my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);
124
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000125 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000126
127 /*
128 * Iterate through the bakery information of each contender to allocate
129 * the highest ticket number for this cpu.
130 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000131 for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
Soby Mathew523d6332015-01-08 18:02:19 +0000132 if (me == they)
133 continue;
134
135 /*
136 * Get a reference to the other contender's bakery info and
137 * ensure that a stale copy is not read.
138 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100139 their_bakery_info = get_bakery_info(they, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000140 assert(their_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000141
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000142 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000143
144 /*
145 * Update this cpu's ticket number if a higher ticket number is
146 * seen
147 */
148 their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
149 if (their_ticket > my_ticket)
150 my_ticket = their_ticket;
151 }
152
153 /*
154 * Compute ticket; then signal to other contenders waiting for us to
155 * finish calculating our ticket value that we're done
156 */
157 ++my_ticket;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000158 my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket);
Soby Mathew523d6332015-01-08 18:02:19 +0000159
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000160 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000161
162 return my_ticket;
163}
164
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100165void bakery_lock_get(bakery_lock_t *lock)
Soby Mathew523d6332015-01-08 18:02:19 +0000166{
Masahiro Yamada019b4f82020-04-02 15:35:19 +0900167 unsigned int they, me;
Soby Mathew523d6332015-01-08 18:02:19 +0000168 unsigned int my_ticket, my_prio, their_ticket;
169 bakery_info_t *their_bakery_info;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000170 unsigned int their_bakery_data;
Masahiro Yamada019b4f82020-04-02 15:35:19 +0900171 bool is_cached;
Soby Mathew523d6332015-01-08 18:02:19 +0000172
Soby Mathew3700a922015-07-13 11:21:11 +0100173 me = plat_my_core_pos();
Masahiro Yamada019b4f82020-04-02 15:35:19 +0900174 is_cached = is_dcache_enabled();
Soby Mathew523d6332015-01-08 18:02:19 +0000175
176 /* Get a ticket */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100177 my_ticket = bakery_get_ticket(lock, me, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000178
179 /*
180 * Now that we got our ticket, compute our priority value, then compare
181 * with that of others, and proceed to acquire the lock
182 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000183 my_prio = bakery_get_priority(my_ticket, me);
184 for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
Soby Mathew523d6332015-01-08 18:02:19 +0000185 if (me == they)
186 continue;
187
188 /*
189 * Get a reference to the other contender's bakery info and
190 * ensure that a stale copy is not read.
191 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100192 their_bakery_info = get_bakery_info(they, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000193 assert(their_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000194
195 /* Wait for the contender to get their ticket */
Soby Mathewa0a897d2015-02-19 16:23:51 +0000196 do {
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000197 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000198 their_bakery_data = their_bakery_info->lock_data;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000199 } while (bakery_is_choosing(their_bakery_data));
Soby Mathew523d6332015-01-08 18:02:19 +0000200
201 /*
202 * If the other party is a contender, they'll have non-zero
203 * (valid) ticket value. If they do, compare priorities
204 */
205 their_ticket = bakery_ticket_number(their_bakery_data);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000206 if (their_ticket && (bakery_get_priority(their_ticket, they) < my_prio)) {
Soby Mathew523d6332015-01-08 18:02:19 +0000207 /*
208 * They have higher priority (lower value). Wait for
209 * their ticket value to change (either release the lock
210 * to have it dropped to 0; or drop and probably content
211 * again for the same lock to have an even higher value)
212 */
213 do {
214 wfe();
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000215 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000216 } while (their_ticket
217 == bakery_ticket_number(their_bakery_info->lock_data));
218 }
219 }
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100220
221 /*
Raghu Krishnamurthyc3c44002020-01-25 19:20:45 -0800222 * Lock acquired. Ensure that any reads and writes from a shared
223 * resource in the critical section read/write values after the lock is
224 * acquired.
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100225 */
Raghu Krishnamurthyc3c44002020-01-25 19:20:45 -0800226 dmbish();
Soby Mathew523d6332015-01-08 18:02:19 +0000227}
228
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100229void bakery_lock_release(bakery_lock_t *lock)
Soby Mathew523d6332015-01-08 18:02:19 +0000230{
231 bakery_info_t *my_bakery_info;
Masahiro Yamada019b4f82020-04-02 15:35:19 +0900232 bool is_cached = is_dcache_enabled();
Soby Mathew523d6332015-01-08 18:02:19 +0000233
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100234 my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);
Soby Mathewf9baaa52016-11-14 17:19:35 +0000235
236 assert(is_lock_acquired(my_bakery_info, is_cached));
Soby Mathew156280c2015-02-20 16:04:17 +0000237
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100238 /*
239 * Ensure that other observers see any stores in the critical section
Raghu Krishnamurthyc3c44002020-01-25 19:20:45 -0800240 * before releasing the lock. Also ensure all loads in the critical
241 * section are complete before releasing the lock. Release the lock by
242 * resetting ticket. Then signal other waiting contenders.
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100243 */
Raghu Krishnamurthyc3c44002020-01-25 19:20:45 -0800244 dmbish();
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000245 my_bakery_info->lock_data = 0U;
246 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Raghu Krishnamurthyc3c44002020-01-25 19:20:45 -0800247
248 /* This sev is ordered by the dsbish in write_cahce_op */
Soby Mathew523d6332015-01-08 18:02:19 +0000249 sev();
250}